Dystroglycanopathies are a subset of muscular dystrophies characterized by a secondary defect in glycosylation of alpha-dystroglycan (α-DG). The diseases have been linked to autosomal-recessive mutations in at least 18 different genes. They include fukutin-related protein (FKRP), fukutin, like-acetylglucosaminyltransferase (LARGE), POMGnT1, POMT1, POMT2, Isoprenoid Synthase Domain Containing (ISPD), Transmembrane protein 5 (TMEM5), β1,3-N-acetylglucosaminyltransferase1 (B3GNT1), glycosyltransferase-like domain containing 2 (GTDC2), β3-N-acetylgalactosaminyltransferase 2 (B3GALNT2) DOLK, GMPPB, DMP2, DMP3 and SGK196. Biochemical studies have established direct evidence for involvement of a number of the genes in glycosylation modifications of α-DG. Fukutin and Fukutin related protein (FKRP) have been recently proposed as Ribitol-5-P transferases that transfer the phosphorated ribitol to the core sugar chain of α-DG. LARGE protein acts as a bifunctional glycosyltransferase, xylosyltransferase and glucuronyltransferase, producing repeating units of [-3-xylose-α1,3-glucuronic acid-β1-] that is the functional glycan chain linking cell membrane protein and extracellular matrix proteins. This LARGE glycan chain is linked to the core O-mannosyl glycans by tandem ribitols. This linkage is critical for muscle health and lack of FKRP function as the result of gene mutations therefore prevents the production of functional glycosylation of α-DG, and disrupts normal interaction between membrane and connective tissues, leading to muscle fiber damage and muscular dystrophy.
Mutations in the FKRP gene cause a wide spectrum of disease from a milder form of limb-girdle muscular dystrophy type 2I (LGMD2I) to severe Walker-Warburg syndrome (WWS), muscle-eye-brain disease (MEB), and congenital muscular dystrophy type 1D (MDC1D). However, little progress has been made for the treatment of the diseases. There is no effective therapy available and only physical therapy and palliative care are being routinely provided as treatment.
The present invention overcomes previous shortcomings in the art by providing pharmaceutical compositions and methods of their use in treating dystroglycanopathy, muscular dystrophy and other disorders.